Even if it's on the second field, it makes sense for the Blacks to host. It would be great to be on the main ground though. The referee keeps track of Yellow Card timings (usually AR1 if available). Reserves etc are all coordinated through the Match Day Table where both clubs run the Rugby Xplorer App to update scores etc. The teams listed in the paper may not be accurate as they're likely sent in on a Thursday lunchtime. But each club has to update their Rugby Xplorer team lists before the game is played which tracks who has played where. Is it perfect? No. Is it open to exploitation? Yes. Is it any different to paper-based team sheets? No.